1. Field of the Invention
The present invention relates to a method and an instrument for measuring a vacuum ultraviolet light beam having a wavelength not longer than 190 nm. Further, the present invention relates to a method for producing a device which method includes exposure treatment using the vacuum ultraviolet light beam and an optical exposure apparatus.
2. Description of a Related Art
In an optical exposure apparatus, a micro-fabrication of a pattern to be transcribed on photo resist, which is coated on a predetermined portion of a substrate, is going on more than ever before, and more improvement of resolution of an optical exposure apparatus is demanded. As a solution for responding to this demand, it is promoted to shorten a wavelength of a light beam for exposure treatment. At the present time, the usable light source that can output a light beam having the shortest wavelength is an F2 (molecular fluorine) laser. The F2 laser beam is a sort of vacuum ultraviolet light beam having a wavelength not longer than 190 nm. And an oscillated wavelength of the F2 laser beam is 157.63 nm, and an oscillated spectral width of the F2 laser beam is not longer than a few pico-meters.
From the above reason, in recent years, an optical exposure apparatus using the F2 laser, which will be called as an F2 laser beam exposure system hereinafter, as a light source for exposure is provided. Also, an instrument for measuring the F2 laser beam, which will be called as an F2 laser beam measuring instrument hereinafter, is provided. An optical unit of each of those instruments includes a fluoride lens. The fluoride lens is a single lens composed from fluorite (CaF2), which is suited for the F2 laser beam. The F2 laser beam tends to be easily absorbed into oxygen. On this account, while the F2 laser beam is transmitted, an inside of a housing enclosing a light detector, an optical unit and so on is evacuated or purged by using nitrogen gas. Nitrogen purge is an operation of removing oxygen gas by using dry nitrogen gas.
By the way, an instrument for measuring a light beam or an optical exposure apparatus should be adjusted such that an optical unit included in the instrument realizes its own aim. This is the same in a conventional F2 laser beam measuring instrument or a conventional F2 laser beam exposure system. However, a focal length of a single lens such as a fluoride lens is different in accordance with a wavelength of a light beam. For example, in the case of a convex fluoride lens having a curvature radius of 90 mm and a diameter of 50 mm, the focal length for a light beam radiated from a low pressure mercury-vapor lamp and having a mercury resonance line (253.65 nm) is 253.65 mm, while the focal length for an F2 laser beam having a wavelength of 157.63 nm is 214.60 mm. On this account, in the conventional F2 laser beam measuring instrument or the conventional F2 laser beam exposure system, other light source except for the F2 laser can not be used for adjustment of an optical unit, for example, adjustment of a position of the fluoride lens.
Therefore, adjustment of the conventional F2 laser beam measuring instrument or the conventional F2laser beam exposure system is carried out as follows:
(1) The inside of the housing enclosing a light detector, an optical unit and so on is evacuated or purged by using nitrogen gas.
(2) An F2 laser beam is transmitted into the inside of the housing which has been evacuated or purged by using nitrogen gas. And the F2 laser beam is focused on the light detector through the optical unit.
(3) Based upon the result obtained by the F2 laser beam focused on the light detector, adjustment of the optical unit including adjustment of a position of the fluoride lens is carried out.
Thus, the adjustment of the optical unit including the adjustment of the position of the fluoride lens must be carried out in the housing which has been evacuated or purged by using nitrogen gas. Therefore, operation of the adjustment is very difficult. This increases difficulty of measurement of the F2 laser beam and prevents the spread of exposure treatment using the F2 laser beam.
In order to solve such a problem, it is proposed that an achromatic lens system designed optimally so as to fulfill achromatic conditions for both an F2 laser beam and another light beam (for example, a mercury resonance line) is substituted for the fluoride lens. In order to produce such an achromatic lens system, at least two materials of glass are required which are different in a dispersion value of a refractive index. However, in the past, fluorite was the only material of glass suited for the F2 laser beam, and therefore, such an achromatic lens system could not be produced.
The present invention has been accomplished in view of those problems. The first object of the present invention is to provide a method and an instrument for measuring a vacuum ultraviolet light beam wherein a position of an optical unit to be used for measuring the vacuum ultraviolet light beam can be easily adjusted so as to quickly measure the vacuum ultraviolet light beam. Further, the second object of the present invention is to provide a method of producing a device and an optical exposure apparatus wherein a position of each of an illumination optical unit and a projection optical unit to be used for exposure treatment by using a vacuum ultraviolet light beam can be easily adjusted so as to quickly carry out the exposure treatment.
In order to solve the above-mentioned problem, a method of measuring a vacuum ultraviolet light beam having a wavelength not longer than 190 nm, according to the present invention, comprises: a first step of passing a regular light beam having a wavelength longer than 190 nm through an optical unit; a second step of adjusting a position of an achromatic lens system included in the optical unit such that the regular light beam which passed through the optical unit is focused on a light detector, the achromatic lens system being composed by combining one single lens produced from fluorite with another single lens produced from fluorine-doped synthetic quartz so as to fulfill achromatic conditions for both the regular light beam and the vacuum ultraviolet light beam; a third step of conducting, after the second step, one of (i) evacuating the inside of a housing for enclosing the optical unit and the light detector and (ii) purging the inside of the housing by using nitrogen gas; and a fourth step of focusing, after the third step, the vacuum ultraviolet light beam which passed through the optical unit on the light detector so as to measure the vacuum ultraviolet light beam.
Further, an instrument for measuring a vacuum ultraviolet light beam having a wavelength not longer than 190 nm, according to the present invention, comprises: a light detector for detecting both a regular light beam having a wavelength longer than 190 nm and the vacuum ultraviolet light beam; an optical unit including an achromatic lens system which is composed by combining one single lens produced from fluorite with another single lens produced from fluorine-doped synthetic quartz so as to fulfill achromatic conditions for both the regular light beam and the vacuum ultraviolet light beam; and a housing for enclosing the optical unit and the light detector in order to conduct one of (i) evacuating the inside of the housing and (ii) purging the inside of the housing by using nitrogen gas when measuring the vacuum ultraviolet light beam.
Furthermore, a method of producing a device by using an illumination optical unit, a photo mask stage for fixing a photo mask in which a desired pattern is formed, a projection optical unit and a substrate stage for fixing a substrate in which a predetermined portion is coated with photo resist each enclosed in a housing, according to the present invention, comprises: a first step of passing a regular light beam having a wavelength longer than 190 nm through the illumination optical unit, the photo mask and the projection optical unit in this order; a second step of adjusting a position of an achromatic lens system included in each of the illumination optical unit and the projection optical unit such that the regular light beam which passed through the illumination optical unit, the photo mask and the projection optical unit in this order is focused on the photo resist, the achromatic lens system being composed by combining one single lens produced from fluorite with another single lens produced from fluorine-doped synthetic quartz so as to fulfill achromatic conditions for both the regular light beam and the vacuum ultraviolet light beam; a third step of evacuating the inside of the housing after the second step; and a fourth step of focusing, after the third step, the vacuum ultraviolet light beam which passed through the illumination optical unit, the photo mask and the projection optical unit in this order on the photo resist in order to expose the photo resist.
Moreover, an optical exposure apparatus according to the present invention comprises: an illumination optical unit including an achromatic lens system which is composed by combining one single lens produced from fluorite with another single lens produced from fluorine-doped synthetic quartz so as to fulfill achromatic conditions for both a regular light beam having a wavelength longer than 190 nm and a vacuum ultraviolet light beam having a wavelength not longer than 190 nm; a photo mask stage, arranged on an output side of the illumination optical unit, for fixing a photo mask in which a desired pattern is formed; an projection optical unit arranged on an output side of the photo mask stage, the projection optical unit including an achromatic lens system which is composed by combining one single lens produced from fluorite with another single lens produced from fluorine-doped synthetic quartz so as to fulfill achromatic conditions for both the regular light beam and the vacuum ultraviolet light beam; a substrate stage, arranged on an output side of the projection optical unit, for fixing a substrate in which a predetermined portion is coated with photo resist; and a housing for enclosing the illumination optical unit, the photo mask stage, the projection optical unit and the substrate stage in order to evacuate the inside of the housing when exposing the photo resist by using the vacuum ultraviolet light beam.
According to the present invention, the position of the achromatic lens system included in the optical unit is adjusted such that the regular light beam which passed through the optical unit is focused on the light detector. The wavelength of the regular light beam is longer than 190 nm and different from that of the vacuum ultraviolet light beam, and therefore, the regular light beam is hard to be absorbed in oxygen and can be transmitted in the air. Accordingly, operation of adjusting the position of the achromatic lens system can be carried out easily in the air. When the vacuum ultraviolet light beam is to be measured, the inside of the housing is evacuated or purged by using nitrogen gas. Since the achromatic lens system has been already adjusted in the predetermined position, the measurement of the vacuum ultraviolet light beam can be carried out quickly.